1. Field of the Invention
The invention pertains to seat structure including a seat bottom supported by a resilient spring biasing force wherein the suspension characteristics of the seat bottom are adjustably determined by varying the value of the biasing force imposed upon the seat bottom.
2. Description of the Related Art
The riding characteristics of vehicle seats, particularly seats utilized with industrial equipment such as tractors, trucks, lift trucks, construction equipment, and the like, have long used spring supported seat bottoms to absorb vibrations, jolts and impacts to improve the comfort of the occupant. Such seat bottoms may be totally supported upon springs, or spring biased linkages, or the seat bottoms may be hinged to a frame at one location and supported by springs at a location remote from the hinge wherein vertical displacement of the seat bottom remote from the hinge is possible to improve the seat's riding characteristics.
Because the weight of a seat occupant may vary by many pounds, such as 150 pounds or more, it is common with spring supported seat bottoms to provide means for adjusting the biasing force imposed upon the seat bottom by the springs in order to provide the shock absorbing and seat movement desired for each weight of occupant. Such adjusting structure usually consists of mechanisms, usually screw operated, which impose a pre-compression or pre-tensioning force upon the seat springs to vary the modulus of elasticity of the spring, either the extension or compression of the spring, depending on the type of spring that is used. Such pre-compression or pre-tensioning of the spring will Change the spring length and affects the operating characteristics of the spring, limiting the seat movement, and further, pre-compression or tensioning of a seat spring to increase its resistance to deflection in order to accommodate a heavier occupant reduces the shock absorbing characteristics of the spring and provides an undesirably high "stiffness" to the seat.
Another disadvantage of spring suspension seats having adjustable biasing force devices arises from the high manual forces required to pre-tension or pre-compress the seat springs, and as such pre-tensioning or compression is accomplished manually, high manual forces must be imposed upon the adjusting structure to achieve the desired spring setting.